Variable volume pump



Oct. 3, 1944. c. H. EDEN ETAL VARIABLE VOLUME PUMP Filed sept. 29, 19424 YSheets-Sheet l L l l Oct. 3, 1944. C` EDEN ET AL 2,359,513

#I VARIABLE VOLUME PUMP Filed Sept. 29, 1942 4 Sheets-Sheet 2Jzyefzfars; 'lzarlfsifazl/ardlden, Ida/ard''feyewsan.

Oct. 3, 1944. Q H EDEN ErAL 2,359,513

VARIABLE VOLUME PUMP Filed Sept. 29, 1942 4 Sheets-Shea?Y 4 anfrZ'd'wrdlf 5760611.90.

ings.

Patented Oct. 3, 1944 UNITED. STATES PA sli-ica 2,359,513 VARIABLEVOLUME PUMP Charles Howard Eden and Edward E. Stevenson,

Los Angeles, Calif.

Application September `Z9, 1942, Serial No. 460,088

10 Claims.

pressure power transmission system such,y as is set out in our copendingapplication, Ser. No.

334,558 led May l1, 1940. It will therefore be described as a pump andwith reference to such a closed circuit system as is set o ut in thatapplication, but without limitation thereto. In such systems, and inmany other situations. there is desired a compact, positively actingpump of the rotary type having little or inappreciable slippage, highefficiency and long life; and also one that may be adjusted to diiferentcapacities at high efciency.

How our present inventionI reaches the desired ends will be bestunderstood from the following detailed description of the preferred andillusv trative design shown in the accompanying draw- In these drawings:Fig. 1 is a central longitudinal sectlon'of anillustrative and typicalpumpstructure embodying vthe invention, the sections. through thetwopump elements which are, shown in Figs. 4"and 5 being taken respectivelyon the lines designated I-I land Ia-Ia in those iigures;

Fig. 2 is an .end elevation, with parts in section on line 2-2 of Fig.1, for illustrative purposes;

Fig. 3 is a cross section on line 3- -3l o f Fig. 1;

Fig. 4 a cross section on line 4-4 of Fig. 1;

Fig. 5 1s a cross section on line 5-5 of Fig. 1;

Fig. 6 is a developed diagrammatic view showing the shapes of the inletand outlet ports;

Fig. 7 is a fragmentary perspective illustrating the formation of theports which are showndiagrammatically in Fig. `6. d4,5

In the drawings a suitable main casing' is illustrated as made up ofparts I and Il which are secured together, as by screws i2, und holdinternally between them the ring I3 in which the two internally ellipticrings M and I are 50 set. Two such elliptic rlngs, with theircooperating pump pistons, 'comprise a pump set which will give asubstantially continuous and uniform delivery of uid under pressure. Thecomplete pump may comprise anysuitable num- 55 ber of these sets; wehere prefer to show a single set, sufllcing to illustrate the invention.

AA rotor 2li is concentrically mounted on bearings 2|` and 22 within thecasing, andls driven from a driving shaft 23 which projects into one` o0arf end of the casingv and is mounted therein on.

bearing 24. The inner enlarged end 23a of shaft 23 hasa clutch or othersuitable driving engagement with rotor 20, as indicated at 25. Rotor hasan internal longitudinal bore 26 through .which a relativelynon-rotatable but adjustable' distributor shaft 30 extends. This shaftcontains inlet and outlet passages and ports and is adjustablelengthwise to change port registry with the cylinders in the rotor, allas vwill be described. The inner end of distributor shaft is carried ina bearing 3| which is carried in the enlarged-inner end of driving shaft23, and the distributor shaft also supported at or near its outer end byhavingv suitable bearing support in the bore 32 of a cylindric casingextension 33 which is secured to casing part l0 by suitable bolts orscrews 34. The distributor shaft 30, and rotor 2li, are thusindependently journalle'd or carried in the casing of the pump, so thatthe contacting surfaces of the distributor shaft and of bore26 of therotor Rotor 20 is provided .with Atwo axially spaced i sets of radialcylinder bores 35, spaced and arrangedas is best shown in Figs. 1,4 and5. Each cylinder' carries a" plunger or piston 36, preferably hardenedand ground to a close' iit in the cylinder and having a rounded hardenedend 36a adapted to engage and follow the concavef elliptic innersurfaceI 4a: or i5a of the two hardenedelliptic rings Il and l5. 'Ihe majoraxes of the two elliptic surfaces Ma and 15a as here shown preferablylie at right angles to each other,.as shown by Figs. 4 and 5. It will bewell understood, without the necessity of further detailed description,how the two sets of pistons are 'reciprocate'd in their cylinders,vvwhen rotor 20 is revolved, by reason of their outer ends following thedescribedielliptic surfaces. The relative arrangement of the two sets ofpistons is such (see Figs. 4 and 5) that each piston of one set. has acorresponding piston in the other set in other, the pistons will beslowly rotated about their own axis as they revolve, thusdistributingthe lubricant and also distributing wear.

A gear pump casing element 40 4lies between' I the inner end of casingextension 33 and casing and is carried in the casing in the bearing 22which has been previously mentioned and also in a bearing' 22a which ismounted in the casing extension 33. The gear element 4| is thus alsojournalled in the casing independently of distributor shaft Sii, so thatthe interfltting surfaces of those two parts are substantially relievedof all wear. Gear element 4I is rotatively interi- Iconnected to rotor2u by any suitable means, such as the clutch indicated at 42. The othergear element 43 ofthe gear pump is mounted within casing 4U on a studshaft M, as shown in Figs. 1 and 3. The inlet to the gear pump. which isalso the initial inlet to the whole pump mechanism, is designated 5t inFigs. 1 and 3, being indicated in dotd lines in Fig. l. The outlet fromthe gear pump is designated 5|' in Figs. 2 and 3.`-

. From the gear pump outlet 5| a pipe or tubing arrangement 52 leads totwo ports 53in casing extension' 33, which communicate with an annularchannel 55 in the inner bore of 33 surrounding distributor shaft 30.Distributor shaft 30 has in it apair of diametrically opposed,longitudinal,A inlet passages 56, and another pair of diametricallyopposed, longitudinal, outlet passages 5l. These passages are preferablyar- Figs. 2, 4 and 5. As illustrated, all these passages are formed asbores extending from the outer deft hand) end of distributor shaft 3o tothe vicinity'of the inner (right hand) end of that shaft. The outletpassages 5l are open at the projecting outer end of the distributorshaft and may there connect with any suitable outlet piping or otherdistribution system as may be desired. In Fig. 2, the two outletpassages 5l 'are diametrically indicated as being'connected by lines 58with a fluid pressure motor 59, and the exhaust of the fluid pressuremotor is indicated as connected by line 60 with .theinitial pump intake50; forming a closed circuit system.

The inlet passages 56 are communicated with the annular recess passage55 by ports 6|, shown in Figs. 1 and 2, so located and of suchlengththat the ports will remain in register with passage 55 throughoutthe longitudinal adjustment movement of distributor shaft 30. The inletof fluid to inlet passages 56 being from the gear pump via passage 55and ports 6I; the outer ends of the bored passages 58 are stopped in anysuitable manner, as byjplugs such as shown at "sz in Fig. 1.

At the transverse plane of each of the piston and cylindersets,"distributor shaftll is provided with a set of two inlet ports 85and two outlet ports-68, these inlet and outlet ports registeringrespectively, with the inlet and outletpassages 56 and 51 as is shown inFigs. l, 4 and 5, and their outer ends are at the outer or peripheralsurface'ofdistrlbutor shaft 30, where their outer ends may be registeredby. the cylinderports 35h during their rotation. These ports 65 and 66are,l

in one of their portions, of equal circumferential extent vabout thecircumference of distributor shaft but in other portions these ports areofunequal circumferential extent, as and for purposes which will behereinafter described. Fig. 1 shows distributor shaft. 30 in such alongi tudinal position that the equal circumferential parts of theseveral ports'are in `.register with rotor cylinders 35, and thesections of Figs. 4 and 5 show those parts of the ports which are ofequal circumferential extent. -The operation of the pump mechanism willfirst be explained as it is with the ports in the positions shown, andthe optional method of operation which may be attained by shifting thedistributor shaft longitudinally will then be explained.

Assuming the counter-clockwise direction ofl rotation indicated by thearrows in Figs. i and 5, the pistons 38 of the two piston sets will moveoutwardly during rotation through the quadrants indicated A and will beforced inwardly during rotation through the quadrants indicated l5. In

4 the aspects shown in Figs. 4 and 5, the inlet ports 65 are of suchcircumferential extent that'the ini ner ends of cylinders will registerwith them -ranged in the relative arrangement shown in f during thetravel of pistons 35 throughout quadrantsvA. Thus, during the travels'of the vpistons and cylinders through quadrants A the pistons may moveout and are moved out by the fiuid pressure which is initially raised bythe' gear pump. The several cylinders of each set thus take-in fluidduring their travels throughout quadrants n.

During and throughout the piston travel through quadrant B they aremoved inwardly by the elliptic track engaged by their outer ends; andoutlet ports 66 are, in the aspect shown in Figs. 4 and 5. so sized andlocatedthat cylinders 35 register with those outlet ports throughout Itravel through quadrants B. The fluid which` has been taken into thecylinders during travel through quadrants A is `forced out underpressure during travel through quadrants B, through theoutlet ports 56and outlet passages 51 and f thence to the high pressure side ofwhatever distributing lines are used (for instance through the lines 58to thekiiuid pressure motor 59) If the pump mechanism is being used in aclosed circuit system, such as here indicated, the'exhaust from motor59, or any other device which is energized by the pump pressure,ilowsthrough the return une soto the mami intake su of the gear pump. Thegear pump is operated at the same speed as the piston pump elements, andit is' designed to be of a capacity to supply the full cawith the innerends of the twosets of rotor cylc' inders 35. The inner open-ends of thecylinders may thus be regarded as ports, registering with the shaftports, and leading to the piston mechanism can'ied by the rotor. Theinner ends of cylinders are preferably vfreduced to form paclty of therotary piston elements at some suitable and relatively low pressure, say20 or 25 lbs. per sq. in. The pressure raised by the gear pump issuillcient to insure that the piston cylinders each take afull charge offluid during their intake strokes, and also sumcient, at least with theaid of centrifugal force, to move the pistons outwardly during theirintake strokes.

Although the pumping capacity of the .gear pump may be made, as nearlyas may be, Just equal to the capactiy of the cylinder and pistonelements, it is preferable to design the gear Inlet and outlet ports andcommunicate, 75 pump for a'slight over-capacity in order to bepreviously takenv in. This expelled portion is sure that the gear pumphas the-desired full capacity of the piston and cylinder elements. Andthat slight over-capacity, if present, may be taken care of by theby-pass arrangements which are hereinafter described. In themode ofoperation which has so far been described, the pump will deliver at itsmaximum capacity per revolation.

Distributor shaft 30 is rotationally stationary but longitudinallymovable,.being splined in the casing extension 35 "by thearrangement-shown at 1D. The outer end of shaft 30 is screw-threaded asshown at H and an internally threaded worm wheel 'l2 engages threads 1|.Worm -wheel l2 has end thrust in one direction .against a bearing 1.3which is set in a member 'Il which forms the end portion of casingextension 33; and may have end thrust bearing in the opposite directionagainst a similar bearing, but ishere shown as bearing simply against abracket'16 attached to member 14. A worin' 11 is mounted in4bearcompressed back into the inlet passages communicating with theinlet port, and is taken care of by the by-pass arrangement to bedescribed.

Each outlet port 66 has. corresponding extensions 66a toward the rightof lesser circumferential extent than the main.port, 66. In thisparticular instance the circumferential, extent of a. port extension 66ais such that each cylinder is inregistry with the port extension durlVing the latter part of` each outlet' quadrant B.

Consequently, in this mode of operation of the l pump, each pistonexpels only about one-half its full capacity into the outlet passages ofthe pump; and the resultant over-all pumping c'apacity of the pump as awhole is .thus reduced to about one-half its full capacity per revolution. The shapes and spacings of the adjacent edges 65h' and 66h of theinlet and outlet ports -are such that the cylinder ports do not registerwith both 6 5 and 66 at thesame time, and such ingsv 18 carried bymember 1I, and a hand wheel 'I6 typifies any suitable. means of rotatingworm 11. By rotating the hand wheel distributor shaft may be movedlongitudinally. In Fig. 1 it is shown in'its limiting right-handposition with relation to the other parts of the pump mechanlsm. It maybe moved to the left through a distance about equal to the, diameter ofcylinders 35. When so moved towardtheeleft the portions of the ports 65and 66 which are directly shown in Figs. 4 and 5 are moved out of theplane of rotationof cylinders and therefore out'of registry with thecylinders, and the portions of the several portsl which lie to the rightin Fig. lare brought into registry with the cylinders 35.

The configurations and relative extents of the port extensions 65a' and66a, and their effect upon the functioning of the pump, may best be-understood from consideration of Figs. 6 and 7.

that any pump capacity intermediate full and half may be had by movingthe distributor shaft appropriately.

The gear pump, which is rotating at even speed with the rotor and'piston assembly, pumps a xed volume of fluid to the piston intake portsper revolution. To take care of the fractional volume which is pumpedback into the intake ports by the pistons in the last described mode ofoperation, and also to take care of any slight excess volume of the pumpin theilrst described mode of operation, a suitable by-pass system' maybe employed. For instance a bypass with a 'loaded valve may beinstalled, leading from any suitable point in the passages between thegear pump and the rotorcylinders, to the initial in- Fig. 6 is adiagrammatic development of the sexies of ports and Fig. 7 is afragmentary pros' pective illustrative of' the port formation. In

Fig-6 the relative direction of rotation (of the rotor and cylinderswith reference ,to the ports),

is indicated by the arrow, andthe successive quadrants of normal intakeand out-put are indicated by the letters A and B. The portions of theports which have been previously described and which in Fig. 1 lie on'the section lines 4 1 and 5-5 are those portions of the `several portswhich lie toward the left in Fig. 6 and are` designated by the numeralsand 66. Each inlet port 65 has an extension 65a toward the right (in adirection axial of distributor shaft 30) and this inlet port extensionis also extended in the direction of rotation by an amount, in thisparticular instance,A equal to something less than half the effectiveregistering Vlength of port 65. Thus, the port extension '65a reachesover into the immediately succeeding outlet quadrant B far enough thatwhen a cylinder in its rotation has passed completely out of registerwith port extension .6 5athat cylinder and its piston is,l

in this particular instance, nearly halfway through the succeedingoutlet quadrant andzthe.

piston is accordingly in about the middle of its fluid expulsion orcompression stroke. Thus, in the operation ofthe pump when portextension 65a1is in register with v thecylindera each cyl'- inder takesin1 its full charge of fluid during the intake quadrant A and thenduring a portion of ciency'is not large when the pump is operating atless than full capacity.

Although the described structure is such, and the relatively rotatingparts are `so journalled, that a' very close lit may be made andmaintained between the distributor shaft and "the 'l other parts toreduce or preclude leakage, suitend of the distributor shaft to precludeleakage able packing glands are Provided at 85 on driving shaft 23 andat 86 on the left hand or outer of any uid from the whole pumpmechanism. The packing gland at 85 makes 'the right-hand end of thepumpfluid-tight. The packing gland at 66 makes the left-hand end of thepump iluidtight and, in particular, prevents any leakage l toward theleft along shaft 30 from the annular passage 55. Leakage toward thelright'from annular passage 55 is precluded by the.` close fit .that ismaintained,between shaft 30 and gear element 4I. And any leakage thatmay occur the succeeding expulsionquadrant B itfexp'els" a proportionatepart of the iluid which has been along or aroundthe shaft within thelimited space between gear element `4I and packing gland 66 is of noconsequence as that leakage only` has egress through the ports l6I whichlead intov the'inlet passages-56.

With the'whole pump mechanism thus packed to prevent'over-all-leakage,the space Sv between rotor 20 and outer casing liI-H may have a sure aslow passage of fluid, usually oil, to the l 'outer piston ends and torings i4 and i5, toiinsure lubrication. At the operating speeds andpressures for which the mechanism is designed and intended,centrifugalforce alone, or that force plus the intake pressure, mayforce the pistons out, even though all leakage pressure is held atpackings 85 and 86. If, however, in any case the operating speeds andpressures are too low to move the pistons out positively, leakage fromspace S may beallowed, either by not using one or both packings 85 and86, or byconnecting space S either with the intake or discharge of thegear pump. For instance a' small pressure venting passage may beprovided at (Fig. l) to vent space S either to atmospheric pressure ortothe intake pressure of the gear pump. .For

instance, the whole pump mechanism may commonly be set in an oilreservoir from which the gear pump intakes and into which the exhaustfrom motor 59 discharges; and vent I0!) may simply discharge into thatreservoir. In such an arrangement the intake pressures on -the pistons36 will always positively force them out no matter how small centrifugalforce may be.

If the gear pump is omittedfrom the mechanism and the piston pumpelements used alone, the initial intake pressure to the pistons 'may bemaintained high enough` either in a closed or open system, to insurefull outward movement of the pistons and the taking of full charges.

Although the whole mechanism has beendescribed as functioning tocompress a fluid, acting as a pumpthe same mechanism may be used as almotor simply by inverting its operation. If pressure fluid be appliedat the high pressure side of the. mechanism (at what has been describedas the high pressure outlet) and a lower pressure be maintained at thelow pressurey side (that has been described as the initial inlet of thepump) the course of fiuid'through the mechanism will be reversed and themechanism will act as a motor to deliver` power at shaft v23.v In suchuse the gear pump unit may if desired be dispensed with, as it also'mayin some circumstances when using the mechanism as a pump.

But if, as a motor, the gear unit is retained, a

two-stage mechanism results, just as there are two stages in thedescribed pump.

Further the mechanism is applicable, either as pump or motor, to lgasfluid as well as liquid. The illustrated form has been particularlydesigned for use with liquid, but the mechanism is nation, althoughpreferred, is merely 'illustres tlve of various and well known forms ofrotary pump or motor mechanisms that' maybe used. In other aspectshowever, a unit having alternating intake and expulsion `strokes forms acharacteristic part of the invention; and the described mechanism ispreferred.

We claim:

1. A fluid pressure mechanism which includes a rotor having an axialbore, a port at the bore surface, and mechanism which takes and expelsfluid through said port during revolution of the port through successivevangles of rotation, and which includes a relatively' non-rotating axialdistributor shaft with an inlet `and an outlet port at the shaftperiphery adapted to be registered successively by the rotor port,characterized further in that: the distributor shaft is longitudinallymovable, the-several distributor ports l have two parts which lierespectively in two longitudinally spaced planes normal of the shaftaxis, the parts of the portswhich lie in one said plane beingsubstantially equal in circumferential extent-and the parts of the portswhich lie in the other plane being one relatively longer and onerelatively shorter in circumferential extent.

2. A fluid pressure mechanism which includes a rotor having an axialbore, a port at the bore surface, and mechanism which takes and expelsiiuid through said port during revolution of the port through successiveangles of rotation, and which includes-a relatively non-rotating axialvdistributor shaft with an linlet and an outlet port at the shaftperipheryadapted to be registered successively by .the rotor port,charactershorter. e

` ing, a rotor with fluid pressure piston mechanism and having aninternal non-rotative longitudinally movable distributor shaft withinlet and outlet passages and ports communicating with the rotormechanism; the combination of a rotary gear pump of two gear velementsone of which is journalled in the casing concentrically about thedistributor shaft in a position longitudinally spaced from the rotor,rotary coupling means between said gear element and the Vrotorindependent of the distributor shaft, and a conduit connecting theoutlet of the gear pump and the inlet passage'of the distributor shaft,the distributor shaft being longitudinally movable through both theVrotor and said concentrically journalled gear. 4. In a fluid pressuremechanism, a. casing, a central longitudinal distributor shaftnon-rotatively mounted in the casing for longitudinal movement therein,a rotor journalled in the casing concentrically about 'the' distributorshaft,

, piston mechanism associated with the rotor, the

dis'tributorshaft having longitudinal inlet and outlet passages andtransverse ports communieating with the proton a gear pump of two gearelements mounted in the-casing, journals supporting one' of the gearelements in Athe casing concentrically about the distributor shaft andin av position longitudinally spaced from the rotor, meansrotatively-coupling the rotor and said gear element independently of thedistributor shaft, anda conduitconnecting the outlet of the gear pumpwith the inlet passage of the 'distributor shaft, the distributor shaftbeing longitudinally movable through .both the vrotor and saidconcentrically journalled gear.

5. In fluid pressure mechanism, la casing, a central longitudinaldistributor shaft mounted in the casing to be non-rotative butlongitudinally movable, a centrally bored rotor journalled in the casingconcentrically about thedistributor shaft to rotate thereabout in afixed radial plane, said rotor having ports at its central bore surfacewhich bore surface iits the central distributor shaft closely, thedistributor shaft having longitudinal inlet and outlet passages andhaving inlet and outlet ports at its periphery adapted to be registeredby the rotor ports, each of the shaft ports having two parts cfdifferent circumferential extent adapted selectively to be moved intoregistery with the rotor ports by longitudinal.

movement of the distributor shaft, and means for moving the distributorshaft longitudinally.

6. In fluid pressure mechanism, a casing, a central longitudinaldistributor shaft mounted in face which bore surface nts the centraldistributor shaft closely, the distributor shaft having longitudinalinlet and outlet passages and having inlet and outlet ports at itsperiphery adapted to be registered by the rotor ports, each of the shaftports having two parts of different circumferential extent adaptedselectively to be moved into registry with the rotor ports bylongitudinal movement of the distributor shaft, lmeans for moving thedistributor shaft longitudinally, a gear pump of two gear elementsmounted inthe casing, one of said gear elements having an axial borefitting the distributor'shaft closely but movably, journals for saidgear element in the casing concentric with the shaft, a coupling betweenthat gear element and the rotor, and a conduit connecting the outlet ofthe gear pump with the inlet passage of the distributor shaft.

'7. In fluid pressure mechanism, a casing, a central longitudinaldistributor shaft mounted in the casing to be non-rotative butlongitudinally movable, a rotor having. a central bore closely cylindersin a common radial plane with their inner ends open at the rotor bore,radially reciprocating pistons associated with the rotor and the casingso as to move radially inwardly and outwardly during successive anglesof rotation, the

distributor shaft 'having longitudinal inlet and outlet passagesreaching lto the'vicinity of the plane of the Arotor and having inletand outlet ports at its periphery, each of the shaft ports inner endsopen at the rotor bore, radially reciprocating pistons associated withthe rotor and the casing so as to move radially inwardly and outwardlyduring successive angles of/rotation, the distributor shaft havinglongitudinal inlet the plane of the rotor and having inlet and outlethaving two parts of different circumferential n the casing to benon-rotative but longitudinally .movab1e, 'a' rotor having a centralbore closely but movably fitting the distributor shaft, the rotor beingjournalled in thecasingconcentri cally about the distributor shaft andconstrained to lrotate in a fixed plane, the rotor having radialcylinders in a common radial plane with their ports at vits periphery,each of the shaft ports having two parts of differentcircumferentialextent adapted selectively to be moved into the plane of rotation of therotor cylinders bylongitudinal movement of the shaft, means for movingthe distributor shaft longitudinally, a gear pump of two gear elementsmounted in the casing, one of said gear elements having an axial borefitting the distributor shaft closely but movably, journals for saidgear element in the casing concentric with the shaft, a coupling betweenthat gear element and the rotor, and a conduit connecting the outlet ofthe gear pump with the inlet passage of the distributor shaft.

9. In fluid pressure mechanism, a casing, av

central longitudinal distributor shaft mounted in the easing to be'non-rotative but longitudinally movable, a rotor having a central boreclosely but movably tting the, distributor shaft, the rotor beingJournalled in the casing concentrically about the distributor shaft.4and constrained to rotate in a fixed plane, the rotor having radialcylinders in a common radial plane with their invner ends open at therotor bore, radially recip shaft having one end within the casing in thevicinity of the rotor and its opposite end projecting from one end ofthe casing, a power 'shaft entering the casing at the first mentionedend of the distributor shaft and rotatively directly,

coupled with the rotor, a packing gland in the casing surrounding thepower shaft, a packing gland in the casing surroundingthe. distributorshaft near its projecting end, and means applied to the projecting endof the distributor shaft for moving it longitudinally.

10. In` fluid pressure mechanism, a casing, a

central longitudinal vdistributor shaft .mounted in the casing to benon-rotative but longitudinally movable, a rotor having a central boreclosely but movably fitting the distributor shaft, the rotor beingjournalled inthe casing concentrically about the distributor shaft andconstrainedl to rotate in a fixed plane, the rotor having radialcylinders in a common radial plane` 'with their inner ends open at therotor bore, radially reciprocating pistons associated with the rotor andthe casing so as to move radially inwardly and outwardly duringsuccessive angles of rotation, the distributor shaft having longitudinalinlet and outlet passages reaching to the vicinity of the plane of therotor and having in.. let and outlet ports at its periphery, each of theshaft ports having two parts of different circum- A ferential extentadapted selectively to be moved into the plane of rotation of the rotorcylinders by longitudinal movement of the shaft, the distributor shafthaving oneend within the casing in the vicinity of the rotor and itsopposite end the casing surrounding the distributor shaft near itsprojectinga end, means applied to the projecting end of the distributorshaft for moving it longitudinally, a gear pump of two gear elementsmounted in the casing, one of said gear elements having an axial borefitting the distributor shaft closely but movably, journals mountingsaid gear element in the casing concentric with the distributor shaftand'longitudmally adjacent the side of the rotor that lies toward theprojectingend of the distributor shaft, a direct coupling between thatgear element and the rotor, a lateral port in the distributor shaftextending from its longitudinal inlet passage toits periphery at a"point between said gear element and the endl of the casing fromwhich-the distributor shaft projects, an annular passage in the casingregistered by said last mentioned port. and-a conduit *I connecting theoutlet of the gear pump with the annular passage.

